1. Field of the Invention
The present invention relates to a hearing aid of the type having an estimating device for estimating a usable signal from an input signal disturbed by interference and a signal-processing device for processing the usable signal to form a usable output signal. The present invention also relates to a method for suppressing noise at a hearing aid.
2. Description of the Prior Art
Persons with impaired hearing often have a reduced ability to communicate in noisy situations. To improve the signal-to-noise ratio, methods of noise reduction have been used for some time. For this purpose, in hearing aids the acoustic signal is picked up with the aid of one or more microphones and electrically processed in such a way that the signal-to-noise ratio is improved, and subsequently an interference-suppressed signal is output via an earphone in the auditory canal.
Depending on how the hearing aid is fitted, the acoustic signal may also enter the auditory canal directly, i.e. concurrently with an electrical processing path, and thus impair the desired influence of the electrical signal processing. Typical concurrent signal paths arise, for example, in the case of hearing aids with open supply or ear adapters with venting holes. In particular, it is known that such concurrent signal paths can strongly impair the noise suppression based on the directional microphone method in the low-frequency range to about 1 kHz.
A hearing aid of the above general type is known, for example, from German OS 198 13 512. Noise suppression occurs in this known device with the aforementioned impairment.
In addition, European Application 1 304 902 describes a method for interference elimination of a redundant acoustic signal in which the intensity of the interference is estimated and, dependent on the intensity of the interference, an input signal component is masked.